1. Field of the Invention
The present invention relates to a projector having a reflection type optical modulator.
2. Related Background Art
Hitherto, as such a kind of projector, as shown in FIG. 1, there has been known a projector which is constructed in a manner such that a polarizing beam splitter 3 is arranged on the emission side of a white light which is emitted from a light source 2, plate-shaped first and second dichroic mirrors 4 and 5 are further sequentially arranged in parallel in the reflecting direction of the light by the polarizing beam splitter 3, the dichroic mirrors 4 and 5 are provided for separating the light into the color lights of red, green, and blue, for irradiating the color lights to reflection type first to third liquid crystal panels 1R, 1G, and 1B to form optical images of the respective color lights, and for synthesizing the color optical images which are emitted from the liquid crystal panels 1R, 1G, and 1B, and the synthetic images which were synthesized by the first and second dichroic mirrors 4 and 5 are enlargedly projected to a screen (not shown) through a projection lens system 6 (for instance, a projector as disclosed in the Japanese Laid-open Patent No. 61-13885).
As each of the reflection type liquid crystal panels 1R, 1G, and 1B mentioned above, a panel of an ECB (Electrically Controlled Birefringence) type can be used and those panels have characteristics such that a polarizing plane of an incident light (S polarizing light) is rotated by 90.degree. by an applied voltage according to the image signal for each color.
In the liquid crystal type video projector with the construction as mentioned above, only the S polarizing light in the white light emitted from the light source 2 is reflected by the polarizing beam splitter 3, the S polarizing light is separated into the color lights of red, green, and blue by the first and second dichroic mirrors 4 and 5, and the color lights are irradiated onto the first to third liquid crystal panels 1R, 1G, and 1B corresponding to the color lights. In the light emitted from the light source 2, the P polarizing light which passes through the polarizing beam splitter 3 is directed to a spare liquid crystal panel 10 locating on the emission destination side of the light and is deviated from an optical path. Each of the color lights which are reflected from the liquid crystal panels 1R, 1G, and 1B is either the light having a P polarizing component in which the polarizing plane was rotated or the light having an S polarizing component in which the polarizing plane is not rotated in accordance with each pixel and the image signal. The color lights are again synthesized by the first and second dichroic mirrors 4 and 5 and, thereafter, they are directed to the polarizing beam splitter 3. In the polarizing beam splitter 3, in each color light, the P polarizing component is transmitted and, after that, it passes through the projection lens system 6 and is projected onto the screen (not shown). The S polarizing component is reflected by the polarizing beam splitter 3 and is returned in the direction of the light source 2.
Therefore, the polarizing beam splitter 3 has functions of both of a polarizer and an analyzer for each of the liquid crystal panels 1R, 1G, and 1B. Each of the liquid crystal panels 1R, 1G, and 1B doesn't need a polarizing plate. Thus, a whole construction is further simplified.
However, the above conventional technique has a drawback such that in the white light emitted from the light source, the P polarizing component which is first transmitted through the polarizing beam splitter doesn't contribute to the projection of an image at all and a using efficiency of the light from the light source is low.